A video from YouTube channel Numberphile demonstrates a classic “pick a card, any card” trick complete with the “is this your card?” moment.

And while it seems like the mechanism must involve some sleight of hand or another clever magician’s illusion, it’s actually all down to maths.

It’s all down to the mechanics of the trick. There are only 21 cards, which are dealt into three rows of seven.

Because this is done three times and the cards are then resorted, it’s possible – as the video explains – to ensure the correct card eventually ends up in the same position in the deck – position number 11 – every time you perform the trick.

You can then add your own flourishes to the reveal – and your audience will never know you’ve baffled them with simple maths.